Persistent Peer IDs in libp2p JavaScript

There's a `loadOrCreateSelfKey` function which you can use to load the key from a persistent datastore (fs).

It's documented here: https://github.com/libp2p/js-libp2p/tree/4420fad686921f88785...

I'll be sure to update the docs to include an example in the config docs.

Damn that's nice, saved me at least a couple of hours of work

this is nowhere to be found in the docs. great stuff